The first purpose of this proposal is to study rats, with or without secondary hyperparathyroidism, fed a calculus-producing diet, to determine whether an underlying skeletal problem causes accelerated alveolar bone destruction in the presence of local oral irritants. The second purpose is to study rats, with or without secondary hyperparathyroidism, in whom orthodontic tooth movement has been undertaken, to determine whether an underlying skeletal problem causes a poor response to orthodontic tooth repositioning. The third purpose is to investigate the relationship of parathormone and vitamin D in controlling bone cell proliferation. In all experiments we plan to study bone cell proliferation which, if disturbed, might explain any observed abnormalities. We will conduct studies of periodontal ligament fibroblasts and maxillary and mandibular endosteal bone cells in this work. We plan to use tritiated thymidine (3HTdR), a label of DNA-synthesizing cells, in rats killed from one hour to five days after 3HTdR injection. We will then do autoradiography of histologic sections of the decalcified bones and cell counts of the sections to estimate proliferation of bone cells and to trace their differentiation into osteoblasts and osteoclasts.